1. Field of the Invention
The present invention relates to a color adjustment system for a display device, and a printed material for use in white point adjustment using the color adjustment system for the display device.
2. Description of the Background Art
Some conventional display color adjustment systems use a color sensor to adjust and operate a display device by means of a previously set white point (brightness and chromaticity) as a target value. In this case, it is not easy to ensure compatibility between the target values of the brightness and the chromaticity previously set by a user and various conditions unmanageable by the display device alone such as the color temperature of illumination, illuminance, paper color and the like in a visual environment.
In some work environments for business use, the color temperature of illumination, a color rendering index (Ra) and illuminance are previously managed at constant values, and specifications of printing paper are also previously managed. In ordinary households, offices and the like, however, illumination design intended only for color management is difficult, and the above-mentioned problem becomes more difficult.
In the case of a printed material, for example, when the color temperature of illumination is changed to a lower value (reddish light), the color temperature of the white point of the printed material based on the reflected light thereof decreases, and is also influenced by the paper color (paper white) of sheets of the printed material. The arrangement of such relationships provides the following mathematical relationship: (the spectral distribution of observed light)=(the spectral distribution of an illumination light source)×(the spectral reflectance of paper).
On the other hand, when the influence of illumination is eliminated, for example, during display on a liquid crystal display device, the following mathematical relationship is provided: (the spectral distribution of observed light)=(the spectral distribution of a backlight source)×(the spectral transmittance of a liquid crystal panel (including a color filter)).
The spectral distribution of light observed on a printed material and the spectral distribution of light observed on a display device are significantly difference in shape from each other. As a means for color matching between the two images, a method to be described below is used. Specifically, the method used in this case is such that display on different devices is performed so that the colorimetric values for tristimulus values in a CIE-XYZ color space and the like are equal in a certain visual environment. In this manner, the concept of the conventional method of color adjustment of a display device is to make an adjustment, based on previously determined observation conditions (light sources and illuminance), printing paper and printing conditions, toward previously determined target adjustment values in accordance with these conditions.
A problem in making the color adjustment to a display device in the case of the prior art lies in the fact that improvements and the like in the visual environment including illumination are not easily made in ordinary households. Also, a purpose-built color measurement device (a color sensor) is necessary for the color management using the tristimulus values. The color sensor is one factor that increases costs in color management.
In regard to a correlation between the color matching function defined by CIE 1931 and the like and the color perception of the actual human eye, there is not always a match between the color measured by the color matching function and the actual appearance thereof, depending on the shapes of the spectral distributions of two types of light to be compared. Accordingly, there are cases in which two colors having the same XYZ values are seen differently.
To solve the problems mentioned above, there has been devised a system for adjusting the white point of a display device by comparison with a reference object color (as disclosed, for example, in Japanese Patent Application Laid-Open No. 2005-208982). Also, there has been devised another system for adjusting the white point in such a manner that different color patches of a plurality of colors are displayed and a user selects a color patch that he or she feels to be an achromatic color (as disclosed, for example, in Japanese Patent Application Laid-Open No. 11-178015 (1999)).
Each of the systems disclosed in Japanese Patent Application Laid-Open No. 2005-208982 and in Japanese Patent Application Laid-Open No. 11-178015 (1999) is a system using visual adjustments, but makes an adjustment with the hand of a user, with a color patch (a color pattern) displayed. In this case, the user having given skills, for example an expert in color science, is capable of making the adjustment with accuracy. However, many of the users in ordinary households are not experts in color science, and often find difficulty in color matching using the color pattern. In some instances, there is a likelihood that the color adjustment operation itself is diverged.